Share This

The long-held, but unproven idea that helium-4 enters into an exotic phase of matter dubbed a "supersolid" when cooled to extremely low temperatures has been challenged in a new paper published recently in Science.

Related Articles

Los Alamos National Laboratory researchers Alexander Balatsky and Matthias Graf joined Cornell University physicist J.C. Séamus Davis and others in describing an alternative explanation for behavior of helium-4 that led scientist to believe for nearly 40 years that the substance could hold properties of a liquid and solid at the same time when cooled to near Absolute Zero.

Helium-4 is the same gas used to fill carnival balloons. When cooled to temperatures below minus 452 degrees below zero Fahrenheit, helium-4 becomes a liquid -- and an extraordinary liquid at that. At very low temperatures, helium-4 can become a "superfluid," a liquid without viscosity that can flow unhampered by friction.

When placed under pressure at these low temperatures, helium-4 atoms arrange in an orderly lattice, or solid, which physicists nearly 40 years ago believed could behave in a similarly frictionless manner as a supersolid -- a unique theoretical state of matter in which a bulk lattice of material could move as a single frictionless object.

Physicists came to the idea that helium-4 becomes a supersolid after oscillating liquid helium-4 back and forth in a special apparatus that measured the rotational speed. When the researchers measured these motions under conditions that would induce a solid form of helium-4, they noticed that the oscillation speed increased slightly, as if some part of the mass had come loose and was uninhibited by interaction with the rest of material. This effect was interpreted as evidence of supersolidity, a phase in which some of the mass of a solid does not move with the rest of solid lattice, but rather flows freely through the lattice.

Los Alamos researchers Balatsky and Graf posited that the effect could be described by an entirely different explanation. They believed the change in oscillation speed could have arisen as the result of a gradual "freezing out" of imperfections within the helium-4 lattice. To illustrate on a very basic level, Balatsky uses a rotating egg.

A fresh egg is a mixture of yolk and albumen within a shell. When spun, the interaction of the liquid within the eggshell results in a relatively slow rotation. If the egg is frozen, however, the imperfections within the shell freeze out, and the egg spins much faster -- like the increase in oscillation speed observed in the early torsional oscillation experiments.

To test this simplified analogy, Balatsky, Davis and colleagues devised an experiment using a torsional oscillator that was 10,000 times more sensitive than the ones used in previous experiments. The researchers looked at results of varying temperature at a constant oscillation speed versus results of varying oscillation speeds at constant temperature. They compared the microscopic excitations within solid helium-4 under both conditions and found that the plotted curves were nearly identical.

Perhaps more significantly, the researchers didn't see a sudden, clearly demarked change in the relaxation of microscopic defects at some "critical temperature" during their experiments. Lack of such a sharp demarcation provides evidence against a change in phase of helium-4 to a supersolid.

Instead, it suggests that the earlier observed behavior was the result of everyday physics rather than some exotic behavior.

"While this experiment does not definitively rule out the possibility of the formation of a supersolid in helium-4, the fact that we have provided a reasonable alternative explanation for the observed behavior in earlier experiments weakens the argument that what was being seen was a phase change to a supersolid," Balatsky said.

In addition to Los Alamos researchers Balatsky and Graf, and Cornell physicist Davis, co-authors of the paper include: Ethan Pratt, formerly of Cornell, but now at the National Institute of Standards and Technology; Ben Hunt and graduate student Vikram Gadagkar at the Massachusetts Institute of Technology; and Minoru Yamashita at Kyoto University.

More From ScienceDaily

More Matter & Energy News

Featured Research

Mar. 3, 2015  By examining the forces that the segments of mosquito legs generate against a water surface, researchers have unraveled the mechanical logic that allows the mosquitoes to walk on water, which may ... full story

Mar. 3, 2015  Researchers have developed a new way of rapidly screening yeasts that could help produce more sustainable biofuels. The new technique could also be a boon in the search for new ways of deriving ... full story

Mar. 3, 2015  Major cities in the UK are falling behind their international counterparts in terms of their use of smart technologies, according to a new study. The research has found that smart cities in the UK, ... full story

Mar. 3, 2015  Scientists have explored friction at the microscopic level. They discovered that the force generating friction is much stronger than previously thought. The discovery is an important step toward ... full story

Mar. 3, 2015  Micro-drones are already being put to use in a large number of areas: These small aircraft face extensive requirements when performing aerial observation tasks or when deployed in the field of ... full story

Mar. 3, 2015  Recent research contributes to the effort to determine the nature of dark matter, one of the most important mysteries in physics. As indirect evidence provided by its gravitational effects, dark ... full story

Mar. 3, 2015  Physicists have shown for the first time that electrons in graphene can be moved along a predefined path. This movement occurs entirely without loss and could provide a basis for numerous ... full story

Mar. 3, 2015  Magnetic vortex structures, so-called skyrmions, could in future store and process information very efficiently. They could also be the basis for high-frequency components. For the first time, a team ... full story

Featured Videos

Forensic Holodeck Creates 3D Crime Scenes

Reuters - Innovations Video Online (Mar. 3, 2015)  A holodeck is no longer the preserve of TV sci-fi classic Star Trek, thanks to researchers from the Institute of Forensic Medicine Zurich, who have created what they say is the first system in the world to visualise the 3D data of forensic scans. Jim Drury saw it in operation.
Video provided by Reuters

Solar Plane Passes New Test Ahead of World Tour

AFP (Mar. 2, 2015)  A solar-powered plane made a third successful test flight in the United Arab Emirates on Monday ahead of a planned round-the-world tour to promote alternative energy. Duration: 01:05
Video provided by AFP

Electric Hydrofoiling Watercraft Delivers Eco-Friendly Thrills

Reuters - Innovations Video Online (Mar. 2, 2015)  The Quadrofoil is a high-tech electric personal watercraft that its makers call a &apos;sports car for the water&apos;. When it hits 10 km/h, the Slovenian-engineered Quadrofoil is lifted above the water onto four wing-like hydrofoils where it &apos;flies&apos; above the surface with minimal water resistance. Matthew Stock reports.
Video provided by Reuters

June 17, 2014  Scientists have presented theoretical calculations which indicate the possible existence of fermionic matter in a previously unknown state -- in the form of a one-dimensional liquid, which cannot be ... full story

Dec. 12, 2012  Physicists from Japan have taken to the skies to grow crystals in zero gravity. Helium crystals were grown using high pressures, extremely low temperatures (0.6K/-272°C) and by splashing them with a ... full story

June 21, 2010  New experiments are casting doubt on previously reported observations of supersolid helium. New research suggests that prior experiments that seemed to show signs of supersolidity were in fact the ... full story

ScienceDaily features breaking news and videos about the latest discoveries in health, technology, the environment, and more -- from major news services and leading universities, scientific journals, and research organizations.